Conditioning of viscose solutions for impregnation and other purposes



Patented Sept. 25, 1934 "UNITED STATES V I 1,974,755, CONDITIONING or VISCOSE SOLUTIONS I FOR IMPREGNATION- AND POSES OTHER PUR- v If. T

Milton 0. Schur, Berlin, N. HQassignorf to Brown Company, Berlin, N. IL, a corporation of Maine NO Drawing. Original application November 1930, Serial No. 494,207.

Divided and this application April 28, 1932, Serial No. 608,149

12 Claims. (Cl; 260-100) This invention relates to viscose solutions or syrups which have been. conditioned with aview toward developing certain desirable properties therein; While not restricted thereto, the vis-V W cose solutions or syrups of the present invention are of 'such character that they canbe applied to great'advantage in the manufactureof articles containing regenerated cellulose.

When it is desired to associate regenerated cellulose into the pores of porous articles such as waterleat papers, fabrics, and moulded or pressed pulparticles, it is preferable to use a viscose solution as the sourceof the regenerated cellulose, both because of its comparatively low cost and the relative'ease with which the cellulose can be ly, wlththe viscosesolution, and with a solution oi cellulose-regenerating agent, preferably with drying of the article between the successive-solution treatments.

I In accordance withthe present invention, I produce an ungelled viscose solution capable of yielding regenerated cellulose upon drying alone. Accordingly, in "producing an article associated with regenerated cellulose, it is necessary to treat the article with onlythe solutionof viscose, and then to effect a drying'of the article. I have found that such a viscose solution may. be .obtained from the usual 'viscose or cellulose x'anthatesolutionyii? the free alkali originally employed to'dissolve the cellulose xanthate is reduced sufiiciently in concentration. For example, I have found that when the usual cellulosexanthate solution containing free alkali in the form of caustic-soda is'largely or completely neutralized or even treated with an excess of neutralizing agent, the xanthate may be rendered unstable, while preserving the solution 'in an ungelled state, so thatvwhenwater is removed from the solution by drying and/or byheat, the xanthate decomposes, liberating the so-called regenerated cellulose. As the alkali is reduced in concentration, the viscose solutionundergoes a-partial splitting or decomposition into sulphur compounds, which in accordance with the present" invention are preferably removed by aerating the solution. Such aeration not onlyreduces the amount of sulphur present in the viscose solution, but lessens the likelihood of contaminating the viscosetreated and dried product Within-smelling compounds.

,::As aspecific exampleof procedure, thetollowing will suflice; To a caustic soda'solution of cellulose xanthate containing, say cellulose, may be added a neutralizing agent, preferably boric acid, until part or all of the free alkali has been neutralized, ,or until there is an excess of boric acid. -The, odor of hydrogen sulphide becomes evident; as neutralization is being effected.- The treated solutionis preferably aerated, as by bubbling air-under pressure thereinto, until the odor has substantially disappeared- The resulting solution is stable in the cold, butis easily gelled when warmed, so that it is preferably kept at or below room temperature prior to being used. It is necessary to preserve the solution in ungelled condition, for itis only assuch that it may be readily absorbed by porous articles to produce products which are :completely impregnated with regenerated cellulose after drying.

While the treated viscose solution may beused for the impregnation of various porous articles, including fabrics and moulded or pressed pulp articles, it is especiallyadvantageousior use in the impregnation of a waterleaf paper intended for use as towelling, for the presence of only about 1% regenerated, cellulose, based on the Weight of dry fiber, in such towelling, not only materially increases the: dry strength of the towelling, but may serve to quadruple or even more greatly to increase its wet strength. For some reason, of which .Iam notnow aware, a wet strength from about 20 to 50% higher has been realized in paper towellingimpregnated with boric-acid-treated viscosesolution than; in similar towelling which has been treated with twosolutions, namely, with an untreated viscose solution and with a solution of cellulose-regenerating, .agent to produce the same amountv of regenerated cellulose in the towelling. 1

One way of adding the viscose solution to the waterleaf paper is to pass the web coming from thedry end of the paper machine through a bath of viscose solution treated in accordance with the present invention, and-then to pass the viscoseimpregnatedweb over'anauxiliary bank of driers,

which dry'the Weband regenerate the cellulose therein. Such practice, while simple, involves double-drying. In the case of a paper machine equipped with a size tub anda secondary bank of driers, the impregnation of the dry web with viscose solution, and the redrying of the viscose-impregnated web present-no difficulties. I prefer, however, to associate the viscose with the web beforeit reaches the; initial drier operatedin combination with the papermachine, thereby permitting savingin steamandin cost of equipment, where 11 additional equipment is necessary or making available the size tub for washing out from the towelling wet soluble substances added thereto along with the viscose solutionfandfurther making available the auxiliary bank of driersfor drying out the Washed web. In this connection, it is to be observed that the towelling is prefervv ably freed from the soluble substances carried thereinto by the viscose solution, as these s'ubthe dry end of the paper machine may be lengthstances may be malodorous, may cause stickiness in the toWelling, and may result in a colored extract when the towelling. is squeezed in. These are various ways open to the addition paper machine, or to the white water draining.

from the paper machine and reused in the beater engine and in the flow box. In these cases, however, it is essential to have a substantially closed, white water system, since otherwise, as is obvious-to one skilled in the art, a very serious loss of viscose may be experienced. Inasmuch as a closed, White water system would necessitate the installation of large-capacity settling basins, to ensure the settling out of a sufiicient quantity of water to be used for the papermachine showers, or alternately, the installation of -filters, I prefer to associate the viscose with the wet web formed from the papermaking stock. The viscose solution may be added to the wet web at different points of its traverse on the wet end of the paper machine. Forinstance, when the paper is being made on the usual Fourdrinierpapermaking machine, the viscose solution may be distributed on the wet web, as by spraying or dripping the solu tion on the web, preferably above a' suction'box.

In this case, it is necessary, for purposes of economy, to reuse the water coming through the suction box and squeezed out at the first press roll, in order to avoid the loss of a considerable amount of viscose which would be present in such water. While the amount of'water' which must be recovered and handled in such case is'much less than that in the methods hereinbefore outlined, nevertheless there is a considerable reduction in the amount of water carried by the Wet web immediately before and after the'first press roll,-such a reduction, in fact, that the amount of water squeezed out from the wet web by the press 'roll may be much greater than thatwhich can be convenientlyconsumed in the preparation of the viscose solution. The preferred way of associating the viscose solution with the wet web is between two press-rolls, as-"in such case'the volume of water containing viscose squeezed from the web is comparatively small and can be readily practically entirely consumed in the preparation of a viscose solution of the concentration desired for application to the wet web. I have observed that as the viscose-impregnated web comes off the drier of the paper machine, it may be but very little higher in wet strength than similar paper lackin g'the presence of viscose therein. If, however, the viscose-impregnated paper is subjected to a temperature of, say, 212 F. for a few minutes, sayfive minutes or longer, the ultimate wet strength of such paper is realized. By ultimate wet strength, I mean the wet strength which is developed in the viscose-impregnated paper when it is stored for one or two days after it has come oif the paper ma chine. My theory is that at'the 'high speed of the drier of the paper machine. tion of cellulose in the paper evidently continues paper machine operation, the temperature which the viscose-impregnated paper attains is not very highfor an appreciable length of time, and consequently the regeneration of cellulose in the paper is incomplete when the paper issues from The regeneraatroom temperature, and reaches completion at this temperature in one or two days. If desired,

ened, that is, provided with a larger number of drier drums, so that the viscose-impregnated paper acquires a'temperature conducive to the maximum wet strength therein as it comes off the machine. Or, if desired, the paper machine may be run at such a rate of capacity permitting the attainment of the maximum wet strength in the paper as fast as it is taken off from the machine.

Thespecific example of treating viscose solutions hereinbefore given, involving the use of boric acid as the neutralizing agent for the free alkali of the solution, is preferable, for the reason that up to date a boric-acid-treated viscose has been found to' impart maximum wet strengths to papers treated therewith. The finding that boric acid produces best results is entirelyempirical, for the free alkali in the viscose solution may be neutralized with other agents, such as alum, ammonium salts, carbon dioxide, sodium bicarbonate, acetic acid, sulphurous acid, and the like, or with combinations of such agents. For example, to a xanthate solution containing, say, about 1% cellulose, may be added an ammonium salt to neutralize the free alkali through the liberation of ammonia. The solution thus treated may be aerated to remove ammonia and volatile sulphides. It might be reasoned that neutralizing agents, such. as ammonium chloride, might be preferable to boric acid, because of their inactivity upon regenerated cellulose, but such is not the case. Inasmuch as the regeneration of cellulose from Xanthate occurs in a complex colloidal system, it might well be that the borate ion has a specific effect on the course of the regeneration of the cellulose. The use of alum as the neutralizing agent also has its advantages, not only in that it neutralizes the alkali content of a viscose solution without causing its gelling, but further in that it is comparatively inexpensive and. is a common ingredient used in a paper mill. Very good results have also been obtained by using a mixture of alum and boric acid as the neutralizing agent, in which case alum, being less expensive than boric acid, lowers the cost of treating the viscose solution.

, It is-my theory that the cellulose xanthate undergoes decomposition or break-down during drying and/ or heating to regenerate cellulose, and that this break-down is promoted by the presence of the alkali salts resulting from the neutralization of the free alkali content of the viscose solution. 7 During drying of the viscose-solutionimpregnated web, the solution undergoes a pro nounced increase in concentration of alkali salts, which doubtless have a cellulose-regenerating effecton the xanthate, especially'at high concentration. These salts perhaps further tend to precipitate the cellulose xanthate from solution during the drying operation, and in so doing influence the rate of the colloidal interactions accompanied by the regeneration of cellulose. This influence may be reflected in papers of various strengths, but, in any event, it is believed to be beneficial to the ,1 resulting product, Sofar as concerns subject matter, this application is a division of my application Serial No. 494,207, filed November 7, 1930.

What I claim is:

1. An ungelled viscose solution whose free alkali content has been neutralized at least in part with boric acid.

2. An ungelled viscose solution whose free alkali content has been neutralized at least in part with alum.

3. An ungelled viscose solution whose free alkali content has been neutralized with both boric acid and alum.

4. A process step which comprises adding boric acid to a viscose solution until the free alkali content of the solution has been neutralized at least in part.

5. A process step which comprises adding alum to a viscose solution until the free alkali content of the solution has been neutralized at least in part.

6. A process step which comprises adding both alum and boric acid to a viscose solution to neutralize free alkali in such solution.

'7. Process steps which comprise adding boric acid to a viscose solution until the free alkali content of the solution has been neutralized at least in part, and aerating the solution to remove volatile sulphur compounds formed in the solution by neutralization.

8. Process steps which comprise adding alum to a viscose solution until the free alkali content of the solution has been neutralized at least in part, and aerating the solution to remove volatile sulphur compounds formed in the solution by neutralization.

9. Process steps which comprise adding both alum and boric acid to a viscose solution to neutralize free alkali in such solution, and aerating the solution to remove volatile sulphur compounds formed in the solution by neutralization.

10. An ungelled, aerated viscose solution whose free alkali content has been neutralized at least in part with boric acid.

11. An ungelled, aerated viscose solution whose free alkali content has been neutralized at least in part with alum.

12. An ungelled, aerated viscose solution whose free alkali content has been neutralized with both boric acid and alum.

. MILTON O. SCI-IUR. 

